Apparatus for sensing position and/or torque

ABSTRACT

An apparatus for measuring relative displacement between a first shaft and a second shaft includes first and second rotor assemblies. The first rotor assembly is coupled to the first shaft and is centered on an axis. The second rotor assembly is coupled to the second shaft. The second rotor assembly has first and second stator plates. Each of the first and second stator plates includes an upper surface and a lower surface. The upper and lower surfaces are parallel. The first and second stator plates include a plurality of teeth extending in a direction radial of the axis. The first and second stator plates form a gap between the lower surface of the first stator plate and the upper surface of the second stator plate. The apparatus further includes at least one magnet having a magnetic field and disposed on the first rotor assembly and a sensing device disposed within the gap for sensing a magnetic flux of the magnetic field.

This application claims priority to U.S. Provisional Patent ApplicationSer. No. 60/477,482 filed Jun. 10, 2003, and U.S. Provisional PatentApplication Ser. No. 60/542,511 filed Feb. 6, 2004.

FIELD OF THE INVENTION

The present invention relates generally to apparatus for sensingposition and/or torque and more particularly to an apparatus for sensingangular displacement between first and second rotating shafts.

BACKGROUND OF THE INVENTION

It is frequently important to measure or sense an angular displacementand/or relative torque between first and second shafts. The relativedisplacement may be measured by a small angle displacement sensor. Therelative position may then be used to derive the torque applied betweenthe two shafts.

For example, power steering systems in motor vehicles and the like aredesigned to provide appropriate hydraulic or electrical assist to allowa driver to complete a turn of the motor vehicle. The driver typicallyturns a steering wheel which is connected to a first shaft. The firstshaft is coupled to a second shaft which is connected to a steeringmechanism. The first and second shafts may be coupled by a compliantmember, such as a torsion bar. Typically, the first shaft may rotatewith respect to the second shaft by a predetermined number of degrees,e.g., +/−12 degrees. Mechanical stops may prevent further movement. Theamount of assist is determined as a function of the amount of torquebeing applied to the first shaft.

Many types of position sensors utilize one or more magnets forgenerating a magnetic field. The magnetic circuit typically includes asecond magnetic structure which forms a gap. A sensing device, disposedwithin the gap, detects changes in the magnetic flux which is used as anindication of the relative displacement between the first and secondshafts.

One such system is disclosed in U.S. patent application Ser. No.20040011138, published Jan. 22, 2004 (hereafter “Gandel”). The secondmagnetic structure in Gandel is made up of two ferromagnetic rings, eachhaving a plurality of axially oriented teeth. Each rings includes acircular flux-closing zone, which is parallel to the flux-closing zoneof the other ring. The teeth of the rings are generally perpendicular tothe flux-closing zones and are interleaved.

One inherent problem with the Gandel device is that it is sensitive tomechanical misalignment during assembly. Specifically, the axial teethof the rings require very accurate placement with respect to each other.A deviation in the relative position of the rings and teeth with respectto each other will cause reduced performance of the device. It isdifficult to accurately align the teeth of the rings and to maintaintheir relative position to maintain the correct distance from tooth totooth.

Another disadvantage of the Gandel device is that it is sensitive tomechanical variation during operation. The device is sensitive toangular and parallel changes in the relationship of the two rotors toone another. Mechanical variation in these two directions will causevariation in the output.

Another disadvantage of the Gandel device is an output variation over360°. This variation is caused by the magnetic structure of the deviceand the measurement location of the magnetosensitive elements.

Another inherent problem with the rings of the Gandel device is thatthey are complex and difficult and costly to manufacture.

The present invention is aimed at one or more of the problems identifiedabove.

SUMMARY OF THE INVENTION

In a first aspect of the present invention, a rotor assembly for use ina sensor for measuring relative position between first and second shaftis provided. The rotor assembly includes first and second stator plates.The first stator plate has an upper surface and a lower surface. Thesecond stator plate has an upper surface and a lower surface. The firstand second stator plates include a plurality of teeth extending in adirection radial of an axis. The first and second stator plates form agap between the lower surface of the first stator plate and the uppersurface of the second stator plate. The gap has a uniform thickness. Therotor assembly further includes a retaining member to hold theorientation and spacing of the first and second stator plates relativeto each other.

In a second aspect of the present invention, a rotor assembly for use ina sensor for measuring the relative position between first and secondshafts is provided. The rotor assembly includes a rotor centered on anaxis. The rotor has an inner surface and an outer surface. The outersurface forms at least one slot associated with an outer radius. Theinner surface forms at least one support structure associated with aninner radius.

In a third aspect of the present invention, an apparatus for measuringrelative position between a first shaft and a second shafts is provided.The apparatus includes first and second rotor assemblies. The firstrotor assembly is coupled to the first shaft and is centered on an axis.The second rotor assembly is coupled to the second shaft. The secondrotor assembly has first and second stator plates. Each of the first andsecond stator plates includes an upper surface and a lower surface. Theupper and lower surfaces are parallel. The first and second statorplates include a plurality of teeth extending in a direction radial ofthe axis. The first and second stator plates form a gap between thelower surface of the first stator plate and the upper surface of thesecond stator plate. The apparatus further includes at least one magnethaving a magnetic field and disposed on the first rotor assembly and atleast one sensing device disposed within the gap for sensing a change inthe magnetic field.

BRIEF DESCRIPTION OF THE DRAWINGS

Other advantages of the present invention will be readily appreciated asthe same becomes better understood by reference to the followingdetailed description when considered in connection with the accompanyingdrawings wherein:

FIG. 1A is an illustration of an apparatus for sensing a relativeposition between a first shaft and a second shaft, according to anembodiment of the present invention;

FIG. 1B is an enlarged illustration of the position sensing apparatus ofFIG. 1A;

FIG. 1C is a three-dimensional illustration of the position sensingapparatus of FIG. 1A in a housing;

FIG. 1D is a top view of the apparatus and housing of FIG. 1C;

FIG. 2A is a first cut away view of the apparatus of FIG. 1A;

FIG. 2B is a second cut away view of the apparatus of FIG. 1A;

FIG. 2C is a cut away view of a portion of a rotor assembly of theapparatus of FIG. 1A;

FIG. 2D is a second cut away view of a portion of a rotor assembly ofthe apparatus of FIG. 1A;

FIG. 3A is a three-dimensional view of a portion of a first and secondrotor assembly of the apparatus of FIG. 1A;

FIG. 3B is a diagrammatic illustration of a position sensor and theapparatus of FIG. 1A;

FIG. 3C is a diagrammatic illustration of a position sensor with twosensing devices, according to an embodiment of the present invention;

FIG. 3D is a diagrammatic illustration of a position sensor with twosensing devices, according to an embodiment of the present invention;

FIG. 3E is an exemplary graph illustrating operation of the positionsensor of FIG. 3C;

FIG. 3F is an exemplary graph illustrating operation of the positionsensor of FIG. 3D;

FIG. 4 is a top view of the first and second rotor assemblies of FIG.3A;

FIG. 5 is a side view of the first and second rotor assemblies of FIG.3A;

FIG. 6 is an exemplary graph illustrating angle versus flux density ofthe apparatus of FIG. 1A;

FIG. 7A is a three-dimensional illustration of a first rotor assembly ofthe apparatus of FIG. 1A, according to an embodiment of the presentinvention;

FIG. 7B is a cut away view of the first rotor assembly FIG. 7A;

FIG. 7C is a side view of the first rotor assembly of FIG. 7A;

FIG. 7D is a diagrammatic illustration of a portion of a rotor of thefirst rotor assembly of FIG. 7A;

FIG. 8A is an illustration of a tooth of the second rotor assemblyaccording to an embodiment of the present invention;

FIG. 8B is an illustration of a tooth of the second rotor assemblyaccording to another embodiment of the present invention;

FIG. 8C is an illustration of a tooth of the second rotor assemblyaccording to a further embodiment of the present invention;

FIG. 8D is an illustration of a tooth of the second rotor assemblyaccording to still another embodiment of the present invention;

FIG. 9A is a diagrammatic illustration of a cut away view of a secondrotor assembly of the apparatus of FIG. 1A, according to a firstembodiment of the present invention;

FIG. 9B is a top view of a portion of the second rotor assembly of FIG.9A;

FIG. 9C is a front view of the second rotor assembly of FIG. 9A;

FIG. 10A is a diagrammatic illustration of a cut away view of a secondrotor assembly of the apparatus of FIG. 1A, according to a secondembodiment of the present invention;

FIG. 10B is a top view of a portion of the second rotor assembly of FIG.10A;

FIG. 10C is a front view of the second rotor assembly of FIG. 10A;

FIG. 11A is a diagrammatic illustration of a second rotor assembly ofthe apparatus of FIG. 1A, according to a third embodiment of the presentinvention;

FIG. 11B is a partial top view of the second rotor assembly of FIG. 11A;

FIG. 11C is a front view of the second rotor assembly of FIG. 11A;

FIG. 11D is a top view of the second rotor assembly of FIG. 11A;

FIG. 11E is a three dimensional view of the second rotor assembly ofFIG. 11A;

FIG. 12A is a top view of a square magnet;

FIG. 12B is a side view of the magnet of FIG. 12A;

FIG. 12C is a top view of a plurality of magnets arranged in parallelrows;

FIG. 12D is a side view of the magnet of FIG. 12C;

FIG. 12E is a three-dimensional view of a ring magnet with a pluralityof north-south pole pairs;

FIG. 13 is a diagrammatic illustration of a cross-sectional view of theapparatus of FIG. 1A, according to a first embodiment of the presentinvention;

FIG. 14 is a diagrammatic illustration of a cross-sectional view of theapparatus of FIG. 1A, according to a second embodiment of the presentinvention;

FIG. 15 is a diagrammatic illustration of a cross-sectional view of theapparatus of FIG. 1A, according to a third embodiment of the presentinvention;

FIG. 16 is a diagrammatic illustration of a cross-sectional view of theapparatus of FIG. 1A, according to a fourth embodiment of the presentinvention;

FIG. 17 is a diagrammatic illustration of a cross-sectional view of theapparatus of FIG. 1A, according to a fifth embodiment of the presentinvention;

FIG. 18 is a diagrammatic illustration of a cross-sectional view of theapparatus of FIG. 1A, according to a sixth embodiment of the presentinvention;

FIG. 19 is a diagrammatic illustration of a cross-sectional view of theapparatus of FIG. 1A, according to a seventh embodiment of the presentinvention;

FIG. 20 is a diagrammatic illustration of a cross-sectional view of theapparatus of FIG. 1A, according to an eighth embodiment of the presentinvention;

FIG. 21 is a diagrammatic illustration of a cross-sectional view of theapparatus of FIG. 1A, according to a ninth embodiment of the presentinvention;

FIG. 22 is a diagrammatic illustration of a cross-sectional view of theapparatus of FIG. 1A, according to a tenth embodiment of the presentinvention;

FIG. 23 is a diagrammatic illustration of a cross-sectional view of theapparatus of FIG. 1A, according to an eleventh embodiment of the presentinvention;

FIG. 24 is a diagrammatic illustration of a cross-sectional view of theapparatus of FIG. 1A, according to a twelfth embodiment of the presentinvention;

FIG. 25 is a diagrammatic illustration of a cross-sectional view of theapparatus of FIG. 1A, according to a thirteenth embodiment of thepresent invention;

FIG. 26 is a diagrammatic illustration of a cross-sectional view of theapparatus of FIG. 1A, according to a fourteenth embodiment of thepresent invention;

FIG. 27 is a diagrammatic illustration of a cross-sectional view of theapparatus of FIG. 1A, according to a fifteenth embodiment of the presentinvention;

FIG. 28 is a diagrammatic illustration of a cross-sectional view of theapparatus of FIG. 1A, according to a sixteenth embodiment of the presentinvention;

FIG. 29 is a diagrammatic illustration of a cross-sectional view of theapparatus of FIG. 1A, according to a seventeenth embodiment of thepresent invention;

FIG. 30 is a diagrammatic illustration of a cross-sectional view of theapparatus of FIG. 1A, according to an eighteenth embodiment of thepresent invention;

FIG. 31 is a diagrammatic illustration of a cross-sectional view of theapparatus of FIG. 1A, according to a nineteenth embodiment of thepresent invention;

FIG. 32 is a diagrammatic illustration of a cross-sectional view of theapparatus of FIG. 1A, according to a twentieth embodiment of the presentinvention;

FIG. 33 is a diagrammatic illustration of a cross-sectional view of theapparatus of FIG. 1A, according to a twenty-first embodiment of thepresent invention;

FIG. 34 is a diagrammatic illustration of a cross-sectional view of theapparatus of FIG. 1A, according to a twenty-second embodiment of thepresent invention;

FIG. 35 is a diagrammatic illustration of a cross-sectional view of theapparatus of FIG. 1A, according to a twenty-third embodiment of thepresent invention;

FIG. 36 is a diagrammatic illustration of a cross-sectional view of theapparatus of FIG. 1A, according to a twenty-fourth embodiment of thepresent invention;

FIG. 37 is a diagrammatic illustration of a cross-sectional view of theapparatus of FIG. 1A, according to a twenty-fifth embodiment of thepresent invention;

FIG. 38 is a diagrammatic illustration of a cross-sectional view of theapparatus of FIG. 1A, according to a twenty-sixth embodiment of thepresent invention;

FIG. 39 is a diagrammatic illustration of a cross-sectional view of theapparatus of FIG. 1A, according to a twenty-seventh embodiment of thepresent invention;

FIG. 40 is a diagrammatic illustration of a cross-sectional view of theapparatus of FIG. 1A, according to a twenty-eighth embodiment of thepresent invention;

FIG. 41 is a diagrammatic illustration of a cross-sectional view of theapparatus of FIG. 1A, according to a twenty-ninth embodiment of thepresent invention;

FIG. 42 is a diagrammatic illustration of a cross-sectional view of theapparatus of FIG. 1A, according to a thirtieth embodiment of the presentinvention;

FIG. 43 is a diagrammatic illustration of a cross-sectional view of theapparatus of FIG. 1A, according to a thirty-first embodiment of thepresent invention;

FIG. 44 is a diagrammatic illustration of a cross-sectional view of theapparatus of FIG. 1A, according to a thirty-second embodiment of thepresent invention;

FIG. 45 is a diagrammatic illustration of a cross-sectional view of theapparatus of FIG. 1A, according to a thirty-third embodiment of thepresent invention;

FIG. 46 is a diagrammatic illustration of a cross-sectional view of theapparatus of FIG. 1A, according to a thirty-fourth embodiment of thepresent invention;

FIG. 47 is a diagrammatic illustration of a cross-sectional view of theapparatus of FIG. 1A, according to a thirty-fifth embodiment of thepresent invention;

FIG. 48 is a diagrammatic illustration of a cross-sectional view of theapparatus of FIG. 1A, according to a thirty-sixth embodiment of thepresent invention;

FIG. 49 is a diagrammatic illustration of a cross-sectional view of theapparatus of FIG. 1A, according to a thirty-seventh embodiment of thepresent invention; and

FIG. 50 is a diagrammatic illustration of a cross-sectional view of theapparatus of FIG. 1A, according to a thirty-eighth embodiment of thepresent invention.

DETAILED DESCRIPTION OF THE INVENTION

With reference to the Figures and in operation, an apparatus 10 sensesthe relative position between a first shaft 12 and a second shaft 14.The relative position may then be used to derive the torque appliedbetween the first and second shafts 12, 14.

In the illustrated embodiment, the apparatus 10 may be used in an powersteering system 16 to provide a measurement of input torque generated bya driver turning a steering wheel (not shown). The input torque is usedto provide appropriate hydraulic or electrical assist to allow thedriver to complete a turn with minimal effort, but increased stability.The first shaft 12 is connected to the steering wheel. The second shaft14 is coupled to a steering system (not shown), for example, as a rackand pinion gear mechanism. As is known in the art, a compliant membersuch as a torsion bar 18 couples the first and second shafts 12, 14. Thefirst and second shafts 12, 14 are moveable relative to each otherthrough a predetermined range, e.g., ±8 or ±12 degrees. It should benoted that the range of relative movement will be dependent uponapplication. The present invention is not limited to any given range ofrelative movement.

Mechanical stops 20 restrict further relative movement between the firstand second shafts 12, 14. A position sensor may be used to measurerotation of the first or second shafts 12, 14. The position sensor maybe a contact or non-contact sensor. The apparatus 10 may containedwithin a housing 22, which may also contain portions of the first andsecond shafts 12, 14 and components of the power steering system. Suchsteering systems 16 are well known in the art and are, therefore, notfurther discussed.

In one aspect of the present invention, the apparatus 10 includes afirst rotor assembly 24 and a second rotor assembly 26. The first rotorassembly 24 is coupled to the first shaft 12 and is centered on an axis28. The second rotor assembly 26 is coupled to the second shaft 14. Thefirst and second rotor assemblies 24, 26 are coaxial.

With specific reference to FIGS. 2A, 2B, 7A, 7B, 7C, the first rotorassembly 24 includes a rotor 30 centered on the axis 28. In oneembodiment, the rotor 30 includes a plurality of slots 32. The firstrotor assembly 24 includes a plurality of magnets 34 located in eachslot 32.

The magnets 34 may be affixed or held in place in any appropriate mannersuch as by an adhesive or crimping. In one aspect of the presentinvention, a retaining member 36 may be used along with, or in place of,the adhesive. The retaining member 36 is made from a non-magneticmaterial, such as plastic. In one embodiment, the retaining member 36 isovermolded the combined rotor 30 and magnets 34, once the magnets 34 areinserted into the slots 32.

With specific reference to FIGS. 2A and 2B, the first rotor assembly 24is pressed onto the first shaft 12. As shown, the first shaft 12 mayhave an enlarged portion 38 which forms a press-fit with the first rotorassembly 24.

The first rotor 30 is composed of a soft magnetic material, such as anickel iron alloy. The first rotor 30 may be made using a stampingprocess or may be made from a powdered metal using a sintering processor through a machining process.

The rotor 30 includes an inner surface 40 and an outer surface 42. Theslots 32 are formed in the outer surface 42. The inner surface 40 has anassociated inner radius 44 and the outer surface 42 has an associatedouter radius 46. In between the slots 32, the rotor 30 forms supportstructures 48. The inner radius 44 is defined by the inner surface 40 atthe center of a support structure 48. In one aspect of the presentinvention, the inner radius 44 is greater than outer radius 46.

In the illustrated embodiment, the magnets 34 are disposed evenly aroundthe circumference of the rotor 30. The spacing between, i.e., the widthof the support structures 48, the magnets 34 are approximately the widthof the magnets 34 or slots 32. The support structures 48 serves as thepath the magnetic flux flows through to complete the magnetic circuit onits path through the magnets 34.

As shown, in the illustrated embodiment, top surface of the magnets 34does not protrude beyond the support structures 48 in the axialdirection.

In one embodiment, the rotor assembly 24 includes six square magnets 34,such as shown in FIG. 12A. The front surface of the magnet 34 in FIG.12A is square. In an alternative embodiment, the front surface of themagnet 34 is rectangular.

The front surface of the magnet 34 in FIG. 12A is the North pole of themagnet 34. The back surface of the magnet 34 is the South pole. In theillustrated embodiment i.e., one of the front or back surface of themagnet 34 is adjacent the rotor 30. Four side surfaces adjoin the frontand back surfaces of the magnets 34. At least one pair of edges formedby one of the front and back surfaces and the four side surfaces of themagnets 34 are rounded.

In one embodiment, all of the magnets 34 on the rotor are orientated ina similar manner, i.e., one of the North pole or the South pole is“down”, i.e., adjacent the rotor 30, and the other pole, is “up”. Inanother embodiment, the orientations of the magnets 34 are alternated,one magnet 34 is orientated “up” and the adjacent magnets 34 areorientated “down”.

The first rotor assembly 24 may also include other magnet arrangements.For example, with reference to FIG. 12B, the rotor assembly 24 mayinclude two adjacent rows 50, 52 of magnets 34. Each row 50, 52 mayinclude a plurality of magnets 34 spaced equidistantly around thecircumference of the rotor 30. Each magnet 34 in one of the rows 50, 52may be orientated in the same direction or orientated in the oppositedirection from the adjacent magnets. Alternatively, the rotor assembly24 may include one or more ring magnets 54, as shown in FIG. 12C. Thering magnet 54 has one or more pairs of adjacent poles 56, i.e., eachpair having a North pole and a South pole. The North pole of one pairbeing adjacent the South pole of the next pair. For example, the ringmagnet 54 may have six pairs of North and South poles. The ring magnet54 has an interior bore 58 which may surround the rotor 34. The ringmagnet 54 may be affixed to the rotor 34 by an adhesive and/or theretaining member 36 and/or any suitable means. If more than one ringmagnet 54 is provided, the ring magnets 54 are parallel.

The rotor 34 is designed to eliminate hoop stress. Hoop stress iseliminated by the relationship between the inner radius 44 and the outerradius 46. As shown, the rotor 34 has no sharp corners which will reducewear on any manufacturing tools. In the illustrated embodiment, eachmagnet slot 32 is defined by a plane 60. A centerpoint 62 of the plane60 is tangent to the outer radius 46. Associated with each slot 32 mayalso include stress relief slots 64. Additionally, a non-continuousinner diameter 47 may also eliminate hoop stress.

Returning to FIGS. 2A, 2B, 3A, 4 and 5, the second rotor assembly 26includes a first stator plate 66 and a second stator plate 68. The firstand second stator plates 66, 68 are parallel to each other. As bestshown in FIG. 5, the first stator plate 66 includes an upper surface 66Aand a lower surface 66B. The second stator plate 68 also includes anupper surface 68A and a lower surface 68B. The upper and lower surfaces66A, 66B, 68A, 68B are parallel. The lower surface 66B of the firststator plate 66 faces the upper surface 68A of the second stator plate68, as shown. The first and second stator plates 66, 68 may bemanufactured using a stamping process may be made from a powdered metalusing a sintering process, or may be made using a machining process.

As best shown in FIGS. 3A and 5, in the illustrated embodiment the firststator plate 66 includes a circular base 66C and a plurality of teeth66D extending from the circular base 66C in a radial direction.Likewise, the second stator plate 68 includes a circular base 68C and aplurality of teeth 68D extending from the circular base 68C in a radialdirection.

As discussed below, the teeth 66D, 68D of the first and second statorplates 66, 68 may be in-phase or offset from each other.

In the illustrated embodiment, the first and second plates 66, 68 areplanar. As shown in FIGS. 3A and 5 the upper surface of the teeth 66D,68D is co-planar with the upper surface 66A, 68A of the respectivestator plate 66, 68 and the lower surface of the teeth 66D, 68D isco-planar with the lower surface 66B, 68B of the respective stator plate66, 68. In other words, the teeth 66D on the first stator plate 66 donot axially intersect with the teeth 68D on the second stator plate 68,i.e., do not intersect with a common plane perpendicular to the axis 28.

As shown in FIG. 5, the first and second stator plates 66, 68 form a gap70 between the lower surface 66B of the first stator plate 66 and theupper surface 68A of the second stator plate 68. As shown, the gap 70has a uniform thickness.

With specific reference to FIGS. 2A, 2B, 2C, 2D, in one aspect of thepresent invention, the second rotor assembly 26 includes a retainingmember 72. The retaining member 72 is made form a non-magnetic material,such as plastic. In one embodiment, the retaining member 72 isovermolded the first and second stator plates 66, 68. The first statorplate 66 and the second stator plate 68 are retained by the retainingmember 72 which fixes the relative position thereof. The retainingmember 72 retains the first and second stator plates 66, 68 in apredetermined relationship, i.e., to maintain the size of the desiredgap 70 and the angular relationship between the first and second statorplates 66, 68.

The retaining member 72 also includes an inner bore 78. The retainingmember 72 is slipped over the second shaft 14, the inner bore 78 forminga friction fit with the second shaft 14. The second shaft 14 may alsoinclude a number of splines (not shown) which form a spline interfacewith the retaining member 72. A retaining ring 80 fitted over an outersurface 82 of the retaining member 74 opposite the inner bore 78 may beused also as a redundant feature to retain the retaining member 72 onthe second shaft 14.

With particular reference to FIGS. 1C, 1D, and 2B, the apparatus 10includes at least one sensing device 84 disposed within the gap 70 forsensing a change in magnetic flux. In the illustrated embodiment, thesensing device 84, e.g., a hall effect sensor, is mounted to a circuitboard 86. The sensing device 84 and the circuit board 86 are containedwith a probe housing 88. The probe housing 88 is either mounted to astationery member (not shown) or rotationally mounted to a bearingsurface (not shown) and serves to accurately position the sensing device84 within the gap 70. A wire harness 90 provides power and deliverssignals from the sensing device 84. Alternately or additionally, a wedgegage plate, or screws may be used to assist in accurately positioningthe sensing device 84 in the gap 70.

As discussed above, in the illustrated embodiment, the teeth 66D, 68D ofthe first and second stator plates 66, 68 are offset or out-phase. Themagnetic field measured by the sensing device 84 varies depending on thealignment of the magnets in the first rotor assembly 24 and the teeth68D, 68D. As shown in FIG. 4, the radial gap between the teeth 66D, 68Dand the top of the magnets 34 is greater than the gap between the teeth66D, 68D and the top of the supporting structures 48.

The magnetic circuit formed by the magnets has mainly two regions calledupper magnetic zone formed between upper stator and the magnets andlower magnetic zone formed between lower stator and the magnets. Thedifferential flux between these two zones flows through the measurementslot where magnetosensitive elements sense the field. Hence at no loadtorque condition, both of the zones produce the same amount of flux,hence the differential flux crossing through the gap 70 is zero.Depending on the relative displacement (+/−8 degrees) the differentialflux either flows up or down in the measurement slot. With reference toFIG. 6, an exemplary graph of flux density measured by the sensingdevice 84 as a function of angular displacement between the first andsecond shafts 12, 14 is shown. At zero degrees, no torque is being onthe first shaft 12 and no flux is measured. As torque is applied to thefirst shaft 12, the flux density measured by the sensing device 84increases or decreases depending on the direction of travel of the firstshaft 12. As shown in the example of FIG. 6, the maximum relativedisplacement between the first and second shafts 12, 14 is +/−θ degreeswith an associated −/−G Gauss of flux density variation. It should benoted that the graph of FIG. 6 is exemplary and for illustrativepurposes only.

With particular reference to FIGS. 3C, 3D, 3E, and 3F, two sensingdevices 84 may be used. Any changes in magnetic flux at constantdisplacement between the first and second rotor assemblies 24, 26 over360 degrees will have the same effect on each device 84. The spacing ofthe sensing devices 84 is dependent upon the number of magnetic polesand teeth of the first and second rotor assemblies 84, respectively. Inthe illustrated embodiment, there are six magnets associated with thefirst rotor assembly 24 and six radial teeth in each stator in thesecond rotor assembly 26. Due to this particular magnetic structure, atconstant torque conditions, the differential flux in the measurementzone will vary over 360 degrees. This variation will cause anoscillation of the output over 360 degrees which will appear with afrequency equal to the number of magnetic poles and stator teeth locatedon the first and second rotor assemblies. As shown in FIG. 3C, twosensing devices 84 may be used. In the present embodiment, thisoscillation will have a 6th order ripple and will be referred to as a “6per rev”. This six per rev will appear in the signal from both sensingdevices 84 (T1 and T2). In this case, the T1 and T2 signals haveopposite polarities. The black rectangle inside the Hall sensors 84represents the sensitive area of the device. The output signals areproportional to the normal component of the flux passing through thesensitive area. It is desirable that the oscillation affects the T1 andT2 signals in the same manner at the same time. Because of this, theHall sensors should be separated such that the oscillations in T1 and T2remain in phase (since they are inverted to each other). By placing theoscillations of the T1 and T2 signals in phase, the ripple effect in thecalculated torque signal is minimized. Due to mechanical packaginglimitations with regard to the locations of the sensitive areas of thetwo Hall sensors with respect to each other, a certain phase shiftexists between T1 and T2. This phase shift is shown in FIG. 3C as θ₁.FIG. 3E illustrates the T1 and T2 signals over 360 degrees with nocompensation. In this particular embodiment our goal is to minimize theoscillation in the calculated torque signal. By placing the two Hallprobes 30 degrees apart shown as θ₂ in FIG. 3D, we can put the signalsin phase to minimize the output oscillation calculated in the torquemeasurement. FIG. 3D shows the implementation of this concept in thetorque sensor. R is denoting the radial location of the Hall sensorsfrom the axis of the shaft. FIG. 3F illustrates the T1 and T2 signalsafter appropriately spacing the hall probes to minimize the ripple inthe calculated torque signal.

With particular reference to FIG. 3B, in another aspect of the presentinvention, a non-contacting position sensor 92 may be used with theapparatus 10 for sensing the relative and/or absolute position of thefirst shaft 12 and the second shaft 14. The position sensor 92, which isshown diagrammatically, includes a ring magnet 94 magnetizeddiametrically resulting in two-pole (N-S) configuration. The ring magnet94 and the ring shield 96 are concentric with the second shaft 12 androtate therewith. The relative sensor section can detect 0˜360 degreesin either direction of rotation. A disk magnet 98 magnetized through thediameter and a ring shield 10, which are external to the ring shield 96and fixed relative to the first shaft. The disk magnet is used toprovide absolute position of the shaft since the shaft can rotate ±810degrees. The turns counter section of the sensor rotates in steps of 180degrees revolution of the first shaft or the relative sensor section andconnected there by Geneva wheel gear mechanism. In both sensor sectionthere are two Hall sensors placed at quadrature. They both use sine andcosine signals to extract position information.

The teeth 66D, 68D may have different shapes. Various examples of teeth66D, 68D are shown in FIGS. 8A, 8B, 8C, 8D. However, it should be notedthat the present invention is not limited to any one shape of the teeth66D, 68D.

As discussed above, the teeth 66D, 68D may be in phase or out of phase.If the teeth 66D, 68D are in-phase or aligned, a centerline 104 of theteeth 66D of the first stator plate 66 is aligned with a centerline 104of the teeth 68D of the second stator plate 68. If the teeth 66D, 68Dare out-of phase, than the centerline 104 of the teeth 66D of the firststator plate 66 are offset from the centerline 104 of the teeth 68D ofthe second stator plate 68, as shown in FIGS. 3A and 4.

If the teeth 66D, 68D are out-of-phase, there may be a radial gapbetween edges of the teeth 66D, 68D as shown best in FIG. 4, the edgesof the teeth 66D, 68D may be aligned, or the teeth 66D, 68D may at leastpartially overlap.

For example, in one embodiment the edges of the teeth 66D, 68D of one ofthe first and second stator plates 66, 68 are adjacent with an edge ofone of the teeth 66D, 68D of the other of the first and second plates66, 68. The shape of the teeth 66D, 68D is shown in FIG. 8C and therelationship between the teeth 66D, 68D is shown in FIGS. 11D and 11E.

In another embodiment, at least a portion of the edge of one of theteeth 66D, 68D of one of the first and second plates and at least aportion of the edge of one of the teeth 66D, 68D of the other of thefirst and second plates 66, 68 overlap.

With particular reference to FIGS. 9A, 9B, 9C, 10B, 10C, 1A, 11B, and11C, and 13-50 various, configurations of the second rotor assembly 26are shown using simple diagrammatic illustrations. Similar parts arenumbered the same.

With reference to FIGS. 9A, 9B, 9C, 10A, 10B, 10C, 11A, 11B, and 11C, inanother aspect of the present invention the first and second plates 66,68 include axial members 66E, 68E which extend in opposite directionfrom the circular base 66C 68D of the first and second stator plates 66,68, respectively to form the gap 70. In one embodiment, the axialmembers 66E, 68E extend around the circumference of the circular base66C, 68D of each stator plate 66, 68.

With particular reference to FIGS. 9A, 9B, 9C, the teeth 66D, 68Din-phase. FIG. 9A shows a cross-section view of the teeth 66D, 68D. FIG.9B shows a top-down view of the teeth 66D, 68D. FIG. 9C shows a frontview of the teeth 66D, 68D (from the first rotor assembly 24).

With particular reference to FIGS. 10A, 10B, 10C, the teeth 66D, 68D areout of phase with a gap. FIG. 10A shows a cross-section view of theteeth 66D, 68D. FIG. 10B shows a top-down view of the teeth 66D, 68D.FIG. 10C shows a front view of the teeth 66D, 68D (from the first rotorassembly 24).

With particular reference to FIGS. 11A, 11B, 11C, the teeth 66D, 68D areout-of-phase and have the shape as shown in 8C. In this embodiment, theedges of the teeth 66D, 68D are radially adjacent (see above and FIGS.11D and 11E). FIG. 11A shows a cross-section view of the teeth 66D, 68D.FIG. 11B shows a top-down view of the teeth 66D, 68D. FIG. 11C shows afront view of the teeth 66D, 68D (from the first rotor assembly 24).

FIG. 13 shows an apparatus 10 with a first rotor assembly 24 which aplurality of unipolar magnet 34 in first and second rows 50, 52 and asecond rotor assembly 26 with first and second stator plates 66, 68. Thefirst and second stator plates 66, 68 are planar and in phase.

FIG. 14 shows an apparatus 10 with a first rotor assembly 24 which aplurality of unipolar magnet 34 in first and second rows 50, 52 and asecond rotor assembly 26 with first and second stator plates 66, 68 withaxial members 66E, 68E. The first and second stator plates 66, 68 are inphase.

FIG. 15 shows an apparatus 10 with a first rotor assembly 24 with tworing magnets 34 and a second rotor assembly 26 with first and secondstator plates 66, 68 which are planar. The first and second statorplates 66, 68 are in phase.

FIG. 16 shows an apparatus 10 with a first rotor assembly 24 with tworing magnets 34 and a second rotor assembly 26 with first and secondstator plates 66, 68. Each stator plate 66, 68 includes an axial member66E, 68E. The first and second stator plates 66, 68 are in phase.

FIG. 17 shows an apparatus 10 with a first rotor assembly 24 with a rowof unipolar magnets 34 and a second rotor assembly 26 with first andsecond stator plates 66, 68. The first and second rotor plates 66, 68are planar.

FIG. 18 shows an apparatus 10 with a first rotor assembly 24 with a rowof unipolar magnets 34 and a second rotor assembly 26 with first andsecond stator plates 66, 68. The first and second stator plates 66, 68include an axial member 66E, 68E. the first and second rotor plates 66,68 are out of phase.

FIG. 19 shows an apparatus 10 with a first rotor assembly 24 with firstand second rows 50, 52 of unipolar magnets 34 and a second rotorassembly 26 with first and second stator plates 66, 68. The first andsecond stator plates 66, 68 are out of phase.

FIG. 20 shows an apparatus 10 with a first rotor assembly 24 with firstand second rows 50, 52 of unipolar magnets 34 and a second rotorassembly 26 with first and second stator plates 66, 68. The first andsecond stator plates 66, 68 are out of phase and include an axial member66E, 68E.

FIG. 21 shows an apparatus 10 with a first rotor assembly 24 with a ringmagnet 34 and a second rotor assembly 26 with first and second statorplates 66, 68. The first and second stator plates are out of phase andplanar.

FIG. 22 shows an apparatus 10 with a first rotor assembly 24 with a ringmagnet 34 and a second rotor assembly with first and second statorplates 66, 68. The first and second stator plates are out of phase andinclude an axial member 66E, 68E.

FIG. 23 shows an apparatus 10 with a first rotor assembly 24 with tworing magnets 34 and a second rotor assembly 26 with first and secondstator plates 66, 68. The first and second stator plates 66, 68 are outof phase and planar.

FIG. 24 shows an apparatus 10 with a first rotor assembly 24 with tworing magnets 34 and a second rotor assembly 26 with first and secondstator plates 66, 68. The first and second stator plates 66, 68 are outof phase and include an axial member 66E, 68E.

With reference to FIG. 25-32 in another aspect of the present invention,the first and second stator plates 66, 68 may include axially extendingteeth 66F, 68F. The axially extending teeth 66F, 68F may be interleavedor non-interleaved.

FIG. 25 shows an apparatus 10 with a first rotor assembly 24 with aplurality of unipolar magnets 34 arranged in first and second rows 50,52 and a second rotor assembly 26 with first and second stator plates66, 68. The first and second stator plates 66, 68 are in phase. Eachstator plate 66, 68 includes an axially extending member 66E, 68E and aplurality of axially extending teeth 66F, 68F. The axially extendingteeth 66F, 68F are non interleaving.

FIG. 26 shows an apparatus 10 with a first rotor assembly 24 with tworing magnets 34 and a second rotor assembly 26 with first and secondstator plates 66, 68. The fist and second stator plates 66, 68 are inphase. Each stator plate 66, 68 includes an axially extending member66E, 68E and a plurality of axially extending teeth 66F, 68F. Theaxially extending teeth 66F, 68F are non interleaving.

FIG. 27 shows an apparatus 10 with a first rotor assembly 24 with aplurality of unipolar magnets 34 arranged in first and second rows 50,52 and a second rotor assembly 26 with first and second stator plates66, 68. The first and second stator plates 66, 68 are out of phase. Thefirst and second stator plates 66, 68 are planar and include a pluralityof axially extending teeth 66F, 68F. The axially extending teeth 66F,68F are interleaving. Alternatively, a single row of magnets 34 may beprovided.

FIG. 28 shows an apparatus 10 with a first rotor assembly 24 with aplurality of unipolar magnets 34 arranged in first and second rows 50,52 and a second rotor assembly 26 with first and second stator plates66, 68. The first and second stator plates 66, 68 are out of phase. Eachstator plate 66, 68 includes an axially extending member 66E, 68E and aplurality of axially extending teeth 66F, 68F. The axially extendingteeth 66F, 68F are interleaving. Alternatively, a single row of magnets34 may be provided.

FIG. 29 shows an apparatus 10 with a first rotor assembly 24 with a ringmagnet 34 and a second rotor assembly 26 with first and second statorplates 66, 68. The first and second stator plates 66, 68 are out ofphase. The stator plates 66, 68 include a plurality of axially extendingteeth 66F, 68F. The axially extending teeth 66F, 68F are interleaving.

FIG. 30 shows an apparatus 10 with a first rotor assembly 24 with a ringmagnet 34 and a second rotor assembly 26 with first and second statorplates 66, 68. The first and second stator plates 66, 68 are out ofphase. Each stator plate 66, 68 includes an axially extending member66E, 68E and a plurality of axially extending teeth 66F, 68F. Theaxially extending teeth 66F, 68F are interleaving.

FIG. 31 shows an apparatus 10 with a first rotor assembly 24 with firstand second ring magnets 34 and a second rotor assembly 26 with first andsecond stator plates 66, 68. The stator plates 66, 68 are out of phaseand include a plurality of axial extending teeth 66F, 68F. The axialextending teeth 66F, 68F are interleaving.

FIG. 32 shows an apparatus 10 with a first rotor assembly with first andsecond ring magnets 34 and a second rotor assembly 26 with first andsecond stator plates 66, 68. The first and second stator plates 66, 68are out of phase. The first and second stator plates 66, 68 includeaxial extending members 66E, 68E and a plurality of axial extendingteeth 66F, 68F. The axially extending teeth 66F, 68F are interleaving.

In another aspect of the present invention the first and second statorplates 66, 68 include a plurality of inwardly extending angular teeth66G, 68G or outwardly extending angular teeth 66H, 68H. FIGS. 33-50 showdiagrammatic illustrations of an apparatus with either inwardlyextending angular teeth 66G, 68G or outwardly extending angular teeth66H, 68H. The illustrations show first and second stator plates 66, 68which are either in phase or out of phase, interleaving or notinterleaving teeth 66G, 68G, 66H, 68H and the various magnetarrangements.

Obviously, many modifications and variations of the present inventionare possible in light of the above teachings. The invention may bepracticed otherwise than as specifically described within the scope ofthe appended claims.

1. An apparatus for measuring the relative displacement between a firstshaft and a second shaft, comprising: a first rotor assembly beingcoupled to the first shaft and being centered on an axis; at least onemagnet having a magnetic field and being disposed on the first rotorassembly; a second rotor assembly being coupled to the second shaft, thefirst and second rotor assemblies being coaxial, the second rotorassembly having a first stator plate and a second stator plate, each ofthe first and second stator plates having an upper surface and a lowersurface, the upper and lower surfaces being parallel, the first andsecond stator plates having a plurality of teeth extending in adirection radial of the axis, each tooth having upper surface and alower surface, the upper surface of each tooth being planar with theupper surface of the respective stator plate, the lower surface of eachtooth being planar the lower surface of the respective plate, the firstand second stator plates forming a gap between the lower surface of thefirst stator plate and the upper surface of the second stator plate, thegap having a uniform thickness; and, a sensing device disposed withinthe gap for sensing a magnetic flux of the magnetic field.
 2. Anapparatus, as set forth in claim 1, further comprising a compliantmember coupled between the first and second shafts for allowing relativemovement therebetween.
 3. An apparatus, as set forth in claim 1, furthercomprising a retaining member to hold the first and second stator platesand fixing the relative position thereof, respectively, and beingfixedly coupled to the lower shaft.
 4. An apparatus, as set forth inclaim 3, each stator plate including a circular base section, theplurality of teeth extending from the circular base section.
 5. Anapparatus, as set forth in claim 1, the measuring device being mountedto a stationery member or to a bearing surface.
 6. An apparatus, as setforth in claim 3, the retaining member including a bore for beingpress-fit onto the second shaft.
 7. An apparatus, as set forth in claim3, the retaining member being made from a non-magnetic material.
 8. Anapparatus, as set forth in claim 3, the retaining member being made fromplastic.
 9. An apparatus, as set forth in claim 3, the first and secondstator plates being glued and/or crimped to the retaining member.
 10. Anapparatus, as set forth in claim 3, the retaining member beingovermolded the first and second stator plates.
 11. An apparatus, as setforth in claim 1, wherein the first and second stator plates are madeusing a stamping process or a metal injection molding process or acasting process.
 12. An apparatus, as set forth in claim 1, wherein thefirst and second stator plates are made from a powdered metal using asintering or bonding process.
 13. An apparatus, as set forth in claim 1,the first rotor assembly having a circumference and a plurality of slotsor flats spaced evenly around the circumference, the apparatus includinga plurality of magnets, each magnet being located in one of the slots orflats.
 14. An apparatus, as set forth in claim 13, the plurality ofmagnets being uni-polar.
 15. An apparatus, as set forth in claim 13,each magnet having first and second parallel surfaces and four sidesurfaces, the first and second parallel surfaces being parallel to theaxis, at least one pair of opposite edges formed by one of the sidesurfaces and the first parallel surface being rounded.
 16. An apparatus,as set forth in claim 13, each magnet having first and second parallelsurfaces and four side surfaces, the first and second parallel surfacesbeing parallel to the axis, the first and second parallel surfaces beingrectangular.
 17. An apparatus, as set forth in claim 13, each magnethaving first and second parallel surface and four side surfaces, thefirst and second parallel surfaces being parallel to the axis, the firstand second parallel surface being square.
 18. An apparatus, as set forthin claim 13, the plurality of magnets being in a single row around thecircumference of the first rotor assembly.
 19. An apparatus, as setforth in claim 13, the plurality of magnets being in two rows around thecircumference of the first rotor assembly.
 20. An apparatus, as setforth in claim 1, the first rotor assembly having a circumference, theat least one magnet being a ring magnet.
 21. An apparatus, as set forthin claim 20, further comprising a second ring magnet, the first andsecond ring magnets being in parallel planes perpendicular to the axis.22. An apparatus, as set forth in claim 1, further comprising a secondsensing device having a displacement from the other sensing device suchthat any changes in magnetic flux at constant displacement between thefirst and second rotor assemblies over 360 degrees will have the sameeffect on each device.
 23. An apparatus, as set forth in claim 1, theteeth of the first and second stator plates being in phase.
 24. Anapparatus, as set forth in claim 1, the teeth of the first and secondplates being out of phase.
 25. An apparatus, as set forth in claim 24,an edge of one of the teeth of one of the first and second plates beingadjacent with an edge of one of the teeth of the other of the first andsecond plates.
 26. An apparatus, as set forth in claim 25, at least aportion of the edge of one of the teeth of one of the first and secondplates and at least a portion of the edge of one of the teeth of theother of the first and second plates overlapping.
 27. An apparatus, asset forth in claim 25, at least a portion of the edge of one of theteeth of one of the first and second plates and at least a portion ofthe edge of one of the teeth of the other of the first and second platesforming a gap.
 28. A rotor assembly for use in a sensor for measuringrelative displacement between first and second shafts, comprising: afirst stator plate having an upper surface and a lower surface, theupper and lower surfaces being parallel; a second stator plate having anupper surface and a lower surface, the upper and lower surfaces of thesecond stator plate being parallel, the first and second stator plateshaving a plurality of teeth, the first and second stator plates forminga gap between the lower surface of the first stator plate and the uppersurface of the second stator plate; and, a retaining member to hold thefirst and second stator plates, respectively, the retaining member beingmade from a non-magnetic material.
 29. An apparatus, as set forth inclaim 28, each stator plate including a circular base section, theplurality of teeth extending from the circular base section.
 30. Anapparatus, as set forth in claim 28, the retaining member substantiallyenclosing the first and second stator plates for fixing the relativeposition thereof.
 31. An apparatus, as set forth in claim 28, the teethextending in a direction radial of an axis, each tooth having uppersurface and a lower surface, the upper surface of each tooth beingplanar with the upper surface of the respective stator plate, the lowersurface of each tooth being planar the lower surface of the respectiveplate.
 32. An apparatus, as set forth in claim 28, the teeth of thefirst and second stator plates being in phase.
 33. An apparatus, as setforth in claim 28, the teeth of the first and second plates being out ofphase.
 34. A rotor assembly for use in a sensor for measuring relativedisplacement between first and second shafts comprising: a first statorplate having an upper surface and a lower surface, the upper and lowersurfaces being parallel; a second stator plate having an upper surfaceand a lower surface, the upper and lower surfaces of the second statorplate being parallel, the first and second stator plates having aplurality of teeth, the first and second stator plates forming a gapbetween the lower surface of the first stator plate and the uppersurface of the second stator plate; and, a retaining member to hold thefirst and second stator plates, respectively, the retaining member beingovermolded the first and second stator plates.
 35. A rotor assembly foruse in a sensor for measuring relative displacement between first andsecond shafts comprising: a first stator plate having an upper surfaceand a lower surface, the upper and lower surfaces being parallel; asecond stator plate having an upper surface and a lower surface, theupper and lower surfaces of the second stator plate being parallel, thefirst and second stator plates having a plurality of teeth, the firstand second stator plates forming a gap between time lower surface of thefirst stator plate and the upper surface of the second stator plate;and, a retaining member to hold the first and second stator plates,respectively, the first and second stator plates being glued and/orcrimped to the retaining member.
 36. A rotor assembly for use in anapparatus for measuring the relative position between first and secondshafts, comprising: a rotor centered on an axis, the rotor having aninner surface and an outer surface, the outer surface forming at leastone slot associated with an outer radius, the inner surface forming atleast one support structure associated with an inner radius, the innerradius being larger than the outer radius; and, at least one magnetdisposed in the at least one slot or flat.
 37. An apparatus, as setforth in claim 36, wherein hoop stress is eliminated in the rotorassembly by having the inner radius larger than the outer radius and anon-continuous inner diameter.
 38. A rotor assembly, as set forth inclaim 36, further comprising a retaining member surrounding the rotorassembly for retaining or adhering the at least one magnet in therespective slot or flat.
 39. A rotor assembly, as set forth in claim 38,the retaining member being made from a non-magnetic material.
 40. Arotor assembly, as set forth in claim 36, the rotor having acircumference and a plurality of slots or flats spaced evenly around thecircumference, the rotor assembly including a plurality of magnetslocated in one of the slots or flats.
 41. A rotor assembly, as set forthin claim 40, the plurality of magnets being uni-polar and in a singlerow around the circumference of the first rotor assembly.
 42. Anapparatus, as set forth in claim 40, the plurality of magnets being intwo rows around the circumference of the first rotor assembly.
 43. Anapparatus, as set forth in claim 40, the at least one magnet being aring magnet.
 44. An apparatus, as set forth in claim 38, the retainingmember being overmolded the rotor and at least one magnet.
 45. Anapparatus, as set forth in claim 36, the rotor having a non-continuousinner diameter.